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Elastic light scattering by mature red blood cells (RBCs) was theoretically and experimentally analyzed by use of the discrete dipole approximation (DDA) and scanning flow cytometry (SFC), respectively. SFC permits measurement of the angular dependence of the light-scattering intensity (indicatrix) of single particles. A mature RBC is modeled as a biconcave disk in DDA simulations of light scattering. We have studied the effect of RBC orientation related to the direction of the light incident upon the indicatrix. Numerical calculations of indicatrices for several axis ratios and volumes of RBC have been carried out. Comparison of the simulated indicatrices and indicatrices measured by SFC showed good agreement, validating the biconcave disk model for a mature RBC. We simulated the light-scattering output signals from the SFC with the DDA for RBCs modeled as a disk-sphere and as an oblate spheroid. The biconcave disk, the disk-sphere, and the oblate spheroid models have been compared for two orientations, i.e., face-on and rim-on incidence, relative to the direction of the incident beam. Only the oblate spheroid model for rim-on incidence gives results similar to those of the rigorous biconcave disk model.

A Fourier transform was applied to size an individual spherical particle from an angular light-scattering pattern. The position of the peak in the amplitude spectrum has a strong correlation with the particle size. A linear equation retrieved from regression analysis of theoretically simulated patterns provides a relation between the particle size and the location of the amplitude spectrum's peak. The equation can be successfully applied to characterize particles of size parameters that range from 8 to 180 (corresponding to particle sizes that range from 1.2 to 27.2 [micro]m at a wavelength of 0.633 [micro]m). The precision of particle sizing depends on the refractive index and reaches a value of 60 nm within refractive-index region from 1.35 to 1.70. We have analyzed four samples of polystyrene microspheres with mean diameters of 1.9, 2.6, 3.0, and 4.2 [micro]m and a sample of isovolumetrically sphered erythrocytes with a scanning flow cytometer to compare the accuracy of our new method with that of others. OCIS codes: 170.0170, 290.5850, 290.0290, 100.3190, 120.5820.

We theoretically analyze the aggregation kinetics of colloid particles with several active sites. Such particles (so-called "patchy particles") are well known as chemically anisotropic reactants, but the corresponding rate constant of their aggregation has not yet been established in a convenient analytical form. Using kinematic approximation for the diffusion problem, we derived an analytical formula for the diffusion-controlled reaction rate constant between two colloid particles (or clusters) with several small active sites under the following assumptions: the relative translational motion is Brownian diffusion, and the isotropic stochastic reorientation of each particle is Markovian and arbitrarily correlated. This formula was shown to produce accurate results in comparison with more sophisticated approaches. Also, to account for the case of a low number of active sites per particle we used Monte Carlo stochastic algorithm based on Gillespie method. Simulations showed that such discrete model is required when this number is less than 10. Finally, we applied the developed approach to the simulation of immunoagglutination, assuming that the formed clusters have fractal structure. [ABSTRACT FROM AUTHOR]

Infrared Free electron laser (FEL) is used that induced isotopically selective multiphoton dissociation of PhSiF3 molecules in the gaseous phase. The longer and broader FEL pulse is partially responsible for the lower selectivity. FEL experiments with PhSiF3 performed in a batch mode may also be responsible for the lower selectivity.

Importance of microparticles (MPs), also regarded as extracellular vesicles, in many physiological processes and clinical conditions motivates one to use the most informative and precise methods for their characterization. Methods based on individual particle analysis provide statistically reliable distributions of MP population over characteristics. Although flow cytometry is one of the most powerful technologies of this type, the standard forward-versus-side-scattering plots of MPs and platelets (PLTs) overlap considerably because of similarity of their morphological characteristics. Moreover, ordinary flow cytometry is not capable of measurement of size and refractive index (RI) of MPs. In this study, we 1) employed the potential of the scanning flow cytometer (SFC) for identification and characterization of MPs from light scattering; 2) suggested the reference method to characterize MP morphology (size and RI) with high precision; and 3) determined the lowest size of a MP that can be characterized from light scattering with the SFC. We equipped the SFC with 405 and 488 nm lasers to measure the light-scattering profiles and side scattering from MPs, respectively. The developed two-stage method allowed accurate separation of PLTs and MPs in platelet-rich plasma. We used two optical models for MPs, a sphere and a bisphere, in the solution of the inverse light-scattering problem. This solution provides unprecedented precision in determination of size and RI of individual spherical MPs-median uncertainties (standard deviations) were 6 nm and 0.003, respectively. The developed method provides instrument-independent quantitative information on MPs, which can be used in studies of various factors affecting MP population. © 2015 International Society for Advancement of Cytometry [ABSTRACT FROM AUTHOR]

Magnesium sulfate (MgSO 4 ) is widely used in medicine but molecular mechanisms of its protection through influence on erythrocytes are not fully understood and are considerably controversial. Using scanning flow cytometry, in this work for the first time we observed experimentally (both in situ and in vitro ) a significant increase of H C O 3 − /Cl − transmembrane exchange rate of human erythrocytes in the presence of MgSO 4 in blood. For a quantitative analysis of the obtained experimental data, we introduced and verified a molecular kinetic model, which describes activation of major anion exchanger Band 3 (or AE1) by its complexation with free intracellular Mg 2+ (taking into account Mg 2+ membrane transport and intracellular buffering). Fitting the model to our in vitro experimental data, we observed a good correspondence between theoretical and experimental kinetic curves that allowed us to evaluate the model parameters and to estimate for the first time the association constant of Mg 2+ with Band 3 as K B ~0.07 mM, which is in agreement with known values of the apparent Mg 2+ dissociation constant (from 0.01 to 0.1 mM) that reflects experiments on enrichment of Mg 2+ at the inner erythrocyte membrane ( Gunther, 2007 ). Results of this work partly clarify the molecular mechanisms of MgSO 4 action in human erythrocytes. The method developed allows one to estimate quantitatively a perspective of MgSO 4 treatment for a patient. It should be particularly helpful in prenatal medicine for early detection of pathologies associated with the risk of fetal hypoxia. [ABSTRACT FROM AUTHOR]